Asian researchers develop oil palm waste-to-ethanol process

Researchers in Southeast Asia have identified an approach to producing ethanol using an abundant waste feedstock that could potentially add a significant source of biofuel production from oil palm plantations. Oil palm empty fruit bunch, which is basically the stem of harvested oil palm bunches, is an abundant biomass waste, with 15 million metric tons generated annually by palm oil mills in Malaysia alone. Malaysia and neighboring Indonesia produce about 90 percent of the world’s palm oil. Usually, the waste is burned or used as mulch. Using the right process, however, about half of that waste can be converted to fermentable glucose to achieve a high-yield ethanol.

Suraini Abd-Aziz, a researcher in the department of bioprocess technology at the University Putra Malaysia, and colleagues in Malaysia and Japan set out to examine an efficient process for ethanol production, using glucose recovered during the phase separation process of acid-hydrolyzed oil palm empty fruit bunch.

An efficient, low-temperature phase separation process was previously developed to separate lignin from the biomass. The separated lignophenol derivatives have been used for immobilizing proteins, specifically enzymes, and in fiber composites. Lignin has also been used for power generation at oil palm mills. The new research focused on developing a process to use the remaining cellulose, roughly half by weight of the original biomass.

Acid hydrolysis of the lignocellulose frees the glucose, according to the researchers, which comprises 87.9 percent of the cellulose content in the aqueous phase. The acid hydrolysis, using a 4 percent acid solution, also releases small amounts of the fermentation inhibitors, terpenes and tannins, which were successfully extracted using ethanol-benzene, they said in a research paper. Other compounds were removed in the lignin phase-separation process.

Once the glucose was separated, the researchers used an acid-tolerant Saccharomyces cerevisiea strain for fermentation. Another facet of the research tested different nitrogen sources to use as yeast nutrients, finding both yeast extract and palm oil mill effluent work well, achieving 93 percent and 89 percent of theoretical yield, respectively. Being able to use the mill effluent utilizes another problematic waste stream in the palm oil milling industry.

The paper, “Utilization of Glucose Recovered by Phase Separation System from Acid-hydrolysed Oil Palm Empty Fruit Bunch for Bioethanol Production,” was published in the PertanikaJournal of Tropical Agricultural Science.